Differential pressure switch

ABSTRACT

A differential pressure switch having a bellows mounted in a housing to which pressures are applied to cause the bellows end to be moved by the pressure difference toward and from an open end of the housing. A cap closes the open end and carries a snap action electrical switch that is sealed from the pressures by another bellows mounted transversely to the first, so that movement of the end of the first bellows caused by pressure differences is transmitted to the switch by radial distorting the another bellows.

United States Patent [191 Hellman [451 June 26, 1973 DIFFERENTIAL PRESSURE SWITCH [75] Inventor: Robert R. Hellman, Bridgeport,

Conn.

[73] Assignee: Westport Development &

Manufacturing Company, Inc., Milford, Conn.

22 Filed: Dec. 30, 1970 21 Appl.No.: 102,656

[52] US. Cl 200/83 Y, 200/83 S, 200/83 A, 200/83 W, 200/168 G [51] Int. Cl H01h 35/32, H01h 9/04 [58] Field of Search 200/83 A, 83 C, 83 D, 200/83 Y, 83 S, 83 W, 168 G, 83 R [56] References Cited UNITED STATES PATENTS 2,890,305 6/1959 Gutkowski 200/83 S 3,056,004 9/1962 Davis ZOO/83 Y 3,431,378 3/1969 Hellman ZOO/168 G 3,132,592 5/1964 Rudy et al. 200/83 S 11/1954 Glendinning et a1 200/83 C X 2/1946 Leupold 200/83 S 2,475,069 7/1949 Wood 200/83 C X FOREIGN PATENTS OR APPLICATIONS 634,082 1/1956 Canada 200/83 C 694,892

5/1930 France 200/83 R Primary ExaminerRobert K. Schaefer Assistant Examiner-Robert A. Vendcrhye AttorneyJohnson & Kline [57] ABSTRACT A differential pressure switch having a bellows mounted in a housing to which pressures are applied to cause the bellows end to be moved by the pressure difference toward and from an open end of the housing. A cap closes the open end and carries a snap action electrical switch that is sealed from the pressures by another bellows mounted transversely to the first, so that movement of the end of the first bellows caused by pressure differences is transmitted to the switch by radial distorting the another bellows.

5 Claims, 4 Drawing Figures Pmmmmzs ma 3.742.165

sum 2 or z 1 NVEN TOR.

DIFFERENTIAL PRESSURE SWITCH In heretofore suggested differential pressure switches, a pressure responsive mechanical device, such as a bellows, has one fluid applied to one side thereof and the other fluid applied to the other side, so that the bellows changes its length in direct relation to the difference in value between the pressures of the two fluids. The bellows length for a preselected value of differential pressure is used to actuate an electrical switch which provides an electrical signal that indicates that the preselected differential pressure exists. In many instances, it is also required that the switch be contained so that it be separate from the fluids causing the pressures, and sometimes even that it be in its own environment in an hermetically sealed container.

Pressure switches that have heretofore been proposed to meet these requirements generally have not been found to be completely satisfactory. Some of the objections thereto have been based on the fact that these tend to be quite expensive, are somewhat complex, may be difficult to adjust and repair, are unreliable in maintaining their settings, are physically large and are not susceptible to being altered for use in a plurality of installations having wide pressure ranges.

It is accordingly an object of the present invention to provide a differential pressure switch which obviates most if not all of the heretofore noted deficiencies in differential pressure switches.

Another object of the present invention is to provide a differential pressure switch which has a bellows contained within a hollow body, and in which the switch actuating means and switch are contained within the cap that closes the end of the body with the switch actuating means including another bellows that is mounted transverse to the first bellows.

A further object of the present invention is to achieve the above objects with a differential pressure switch that is extremely simple in construction, relatively economical to manufacture, easy to assemble and adjust and which is reliable over a wide range of pressures and environmental conditions.

In the differential pressure switch of the present invention, there is provided a hollow body having an open end and a tubular bellows having a closed end. The bellows is connected in the body to have fluids separately applied to its interior and exterior, with the closed end of the bellows moving towards and away from the open end of the body in response to differences in the fluid pressures. The open end of the body is closed by thehead of a cap.

A mechanically responsive electrical device, specifically a snap action electrical switch, is positioned on the side of the cap head remote from the bellows and the head contains actuating means for translating movement of the closed end of the bellows into actuation of the switch. In particular, the head of the cap includes another bellows that extends transversely to the movement of the closed end of the first-mentioned bellows, together with actuating arms. One actuating arm is directly engageable by the closed end of the bellows, while the other actuating arm is moved by the first arm and transmits movement of the first arm through the side of the transverse bellows by radially distorting it, and with the radial distortion being used as the mechanical movement for effecting actuation of the snap action switch.

Though the cap closes the end of the body, it is also mounted for relative axial movement therein, such that it may be located with respect to the closed end to be actuated at any desired position of the closed end, with the latter being determined by the difference between the two pressures applied to the bellows. Moreover, to protect the bellows and switch from over-pressures, the cap further includes stop means which limits the extent of movement towards the switch of the closed end, thereby assuring that over-pressures will not deform either the bellows or the switch means.

Other features will hereinafter appear.

In the drawing:

FIG. I is a plan, partly in section, of a differential pressure switch made according to the present invention, shown enlarged about four times.

FIG. 2 is a section taken on line 2-2 of FIG. 1.

FIG. 3 is a section taken on the line 3-3 of FIG. 1.

FIG. 4 is an axial section of another embodiment of a differential pressure switch in which the switch is capable of producing electrical signals for two differential pressures, and is also shown enlarged.

Referring to the drawing, the differential pressure switch shown in FIGS. 1-3 is generally indicated by the reference numeral 10 and includes a tubular hollow body 11 having an open end formed with internal threads 12. Positioned at the other end is a tubular bellows 13 having an open end secured as by welding 14 to the body and having a plug 15 secured to close its other end. A tubular connector 16 is secured to the body 11 and includes a passageway 17 through which a first fluid P1 may be introduced in the direction of the arrow into the interior of the bellows 13. It will be understood that the connector 16 extends to have its end 18 be closely adjacent the plug 15 to limit the movement of the plug 15 theretowards.

An opening 19 extends through the wall of the body, such that a fluid P2 may beintroduced into the body to be on the exterior of the bellows. As it is desired that this specific embodiment of a pressure switch be used by securing it into a tapped opening, the exterior of the body is formed to have exterior threads 20 and a hexagonical periphery 21.

The open end of the body 11 is closed by a cap generally indicated by the reference numeral 22. The cap includes a tubular portion 23 formed with a flange 24 which cooperates with a ledge 25 on the body 11 for effecting sealing therebetween through the use of a sealing member such as an O-ring 26. For securing the cap 22 against the body 11 to both effect the seal and also enable axial movement therebetween, an annular retain-ing nut 27 is provided having threads 28 that cooperate with the threads 12. It will thus be appreciated that, by rotating the nut 27, it cap may be separated from the body or else it may be secured to the body at a selectable location.

The interior end of the tubular portion 23 is closed by a round disk 29 secured thereto as by welding 30. Supported within the cap on the side of the disk 29, remote from the bellows 13, is a snap action switch 31 that is held in position by screws 32 passing through apertures in brackets 33 secured to the interior of the tubular portion. The switch 31 is specifically shown as a snap action switch having an operating lever 34 which, when actuated, causes the switch to shift its movable contact, as is well known in the art, though it will be understood that different positioning sensing devices may be used if desired.

The switch 31 is actuated at a predetermined position of the plug which is attained when the first fluid P] has a selected value of pressure higher than the pressure of fluid P2. The translation of the position of the plug 15 to the operating arm 34 of the switch includes actuating means consisting of an L shaped arm 35 that is pivoted on the disk as at 36 and has a hump 37 that is engageable by the end surface of the plug 15. Extending diametrically across the tubular portion 23 transversely to the movement of the plug 15 and above the disk 29 is another bellows 38 having its ends connected to form a seal with the sides of the tubular portion, it being understood that the ends of the bellows are open and fit within apertures formed in the tubular portion 23 with welding, such as welding 39, about the junction affecting the seal and securement.

A second arm 40 is pivoted, as at 41, on the exterior of the tubular portion and extends through the bellows 38 to be engaged by an end portion 42 of the L shaped arm 35. Intermediate the arm 40 there is a headed rivet 43 that passes through the wall of the bellows 38 and is sealingly secured thereto. The head of the rivet engages the operating arm 34, while the shank of the rivet is engageable by the intermediate portion of the arm With the above construction of the actuating means, it will be understood that, as the pressure of fluid P1 in creases relative to the pressure of fluid P2, at a predetermined differential value, the plug 15 will have moved to engage the hump 37 and pivot the arm 35, which in turn will effect pivoting of the arm 40. The latter pivoting will force the rivet 43 upwardly, radially distorting the bellows 38 and causing actuation of the switch 31. For a more complete description of the manner in which the bellows 38 functions, reference is made to my U.S. Pat. No. 3,431,378.

It will be understood that, by selection of the position of the nut 27 with respect to the body, the differential pressure at which switch 31 is actuated may be easily selected within the limits of the bellows l3 and that the selection automatically compensates for tolerances that may occur during the manufacture of the various parts. Thus the ability to move the cap 22 with respect to the bellows l3 enables the present switch to have a relatively wide range of differential pressures at which it may be adjusted to be actuated and, also, the setting of the part for actuation at the selected differential pressure may be easily achieved and/or modified.

In order to prevent abnormal differential pressures from causing the bellows 13 to be elongated beyond its elastic limits, the disk 29 further includes a pair of outwardly extending plates 44 which serve as stops to limit outward movement of the plug 15. Further, the plates 44 also limit the extent of movement of the arm 35 to prevent excessive overtravel movement on the switch. As shown in FIG. 3, the arm 35 extends between the plates 44, while the pivot 36 thereof includes apertures formed in the plates.

It will accordingly be appreciated that the cap 22 closes off the open end 12 of the body 11 while permitting actuating movement of the plug 15 to be transferred to the operating arm 34 of the switch 31. If desired, the other end of the tubular member 23 may be closed by electrical connector 45 which has electrical pins 46 that extend through the terminal and are sealed thereto by a fluid proof seal. Wires extend from the switch 31 terminals, such as wire 47, to the appropriate end of pins 46 to provide electrical connection between the pins and the switch. Accordingly, by use of the electrical connector 45 and an hermetic seal at the junction 48 between the connector 45 and the tubular portion, the switch 31 becomes contained within an hermetically sealed enclosure.

Referring to FIG. 4, there is shown another embodi ment of the present invention generally indicated by the reference numeral 50. This embodiment includes a tubular body 51 open at both ends, together with a bellows 52 having one end connected as at 53 to the interior of the body and having a plug 54 closing the other end of the bellows. A first passageway 55 directs a fluid P1 to the interior of the bellows, while a second passageway 56 directs another fluid P2 to the exterior of the bellows. I

The present embodiment of the differential switch is designed to provide electrical signals for two different differential pressures and, accordingly, there is provided a first cap 57 and a second cap 58 for closing off the open ends of the body 51. The caps are identical and essentially similar in shape to the cap 22 of the embodiment of a differential switch shown in FIGS. 1-3. Accordingly, referring to the cap 57, it includes a snap action switch 59 together with a transverse bellows 60, operating arms 61 and 62 together with a round disk 63 that closes off the end of a tubular member 64. In addition the disk 63 includes stop plates 65 for limiting leftward movement of the plug 54. A retaining nut 66 serves to adjust and secure the position of the cap with respect to the body 51.

With respect to the cap 58, it similarly has a switch 67 operated by arms 68 and 69 together with a transverse bellows 70 and a nut 71 for securing it to the body 51. It will be appreciated that with this embodiment, at one value of differential pressure wherein P2 may be greater than P1, the switch 59 is actuated at a value selected by the position of the cap in the body, as set by the nut 66, while at a different value of differential pressure where P] may be greater than P2, the switch 67 is operated by the plug 54 moving rightward and pivoting the arms 68 and 69. Again the value of differential pressure at which the switch 67 is operated is set by movement of the nut 71.

It will accordingly be understood that there has been disclosed a differential pressure switch which is composed essentially of two parts, one of the parts including a body that has a pressure responsive member such as a bellows, while the other part includes a cap that carries an electrical switch and actuating means therefor. The two parts are releasably secured together in a manner which enables the position of the cap to be altered with respect to the housing to thereby enable, not only adjustment of the differential pressure at which the switch will be operated, but also to enable setting of the switch to be actuated at that selected pressure. The cap also serves to seal the end of the tubular member,.while the construction of the actuating means prevents either of the fluids that are exerted on the bellows from contacting the switch, thereby hermetically sealing the switch from the two pressures.

Variations and modifications may be made within the scope of the invention and portions of the improvements may be used without others.

I claim:

1. A differential pressure switch comprising a hollow body having an open end, a tubular bellows having a closed end and an open end, means securing the open end of the bellows to the interior of the body with the closed end being directed towards the open end of the .body, means in said body for directing a first fluid to the interior of the bellows and a second fluid to the exterior thereof to have the differential pressure therebetween move the closed end of the bellows toward and away from the open end of the body, a cap secured to the body to close the open end thereof and having a head portion positioned within the body, electrical translating means secured on the cap on the opposite side of the head portion from the bellows, a second bellows mounted on the head portion to extend transversely to the movement of the first-mentioned bellows and actuating means engageable with the closed end and the second bellows for transmitting preselected movement of the closed end through the second bellows to the electrical translating means by radial distortion of the second bellows to thereby effect operation of the electrical translating means, in which the cap is secured to the body by a releasable connecting means, in which the connecting means includes means for relatively moving the cap with respect to the closed end of the bellows along the line of movement of the closed end to thereby enable adjustment of the position of the closed end of the bellows that operates the electrical translating means and in which the releasable connection includes a nut, cooperating threaded connectors on said nut and body and a flange formed on the cap and engageable by the nut.

2. A differential pressure switch comprising a hollow body having an open end, a tubular bellows having a closed end and an open end, means securing the open end of the bellows to the interior of the body with the closed end being directed towards the open end of the body, means in said body for directing a first fluid to the interior of the bellows and a second fluid to the exterior thereof to have the differential pressure therebetween move the closed end of the bellows toward and away from the open end of the body, a cap secured to the body to close the open end thereof and having'a head portion positioned within the body, electrical translating means secured on the cap on the opposite side of the head portion from the bellows, a second bellows mounted on the head portion to extend transversely to the movement of the first-mentioned bellows and actuating means engageable with the closed end and the second bellows for transmitting preselected movement of the closed end through the second bellows to the electrical translating means by radial distortion of the second bellows to thereby effect operation of the electrical translating means, in which the cap is secured to the body by a releasable connecting means, in which the connecting means includes means for relatively moving the cap with respect to the closed end of the bellows along the line of movement of the closed end to therebyenable adjustment of the position of the closed end of the bellows that operates the electrical translating means, in which there is compressible sealing means between the cap and the body and in which the releasable connection causes compression to be exerted on the sealing means to effect a seal.

3. A differential pressure switch comprising a hollow body havingan open end, a tubular bellows having a closed end and an open end, means securing the open end of the bellows to the interior of the body with the closed end being directed towards the open end of the body, means in said body for directing a first fluid to the interior of the bellows and a second fluid to the exterior thereof to have the differential pressure therebetween move the closed end of the bellows toward and away from the open end of the body, a cap secured to the body to close the open end thereof and having a head portion positioned within the body, electrical translating means secured on the cap on the opposite side of the head portion from the bellows, a second bellows mounted on the head portion to extend transversely to the movement of the first-mentioned bellows and activating means engageable with the closed end and the second bellows for transmitting preselected movement of the closed end through the second bellows to the electrical translating means by radial distortion of the second bellows to thereby effect operation of the electrical translating means, in which the cap is secured to the body by a releasable connecting means, in which the connecting means includes means for relatively moving the cap with respect to the closed end of the bellows along the line of movement of the closed end to thereby enable adjustment of the position of the closed end of the bellows that operates the electrical translating means, in which the head portion includes stop means positioned to be engaged by the closed end to limit movement thereof after the translating means operating position and in which the stop means is positioned to limit the movement of the actuating means by the closed end after operation by the closed end.

4. The invention as defined in claim' 3 in which there is .a second cap secured to close the other end of the body and having a head portion, second electrical translating means secured on the second cap on the opposite side of the second head portion from the bellows, a third bellows mounted on the second head portion to extend transversely to the movement of the firstmentioned bellows and second actuating means engageable with the closed end and the third bellows for translating preselected movement of the closed end through the third bellows to the second electrical translating means by radial distortion of the third bellows to thereby effect operation of the second electrical translating means and in which the head portion of the secend cap carries stop means for limiting movement of the closed end andactuating means after operation of the second electrical translating means.

5. The invention as defined in claim 4 in which the second cap is secured to the body by independently operable releasable connecting means. 

1. A differential pressure switch comprising a hollow body having an open end, a tubular bellows having a closed end and an open end, means securing the open end of the bellows to the interior of the body with the closed end being directed towards the open end of the body, means in said body for directing a first fluid to the interior of the bellows and a second fluid to the exterior thereof to have the differential pressure therebetween move the closed end of the bellows toward and away from the open end of the body, a cap secured to the body to close the open end thereof and having a head portion positioned within the body, electrical translating means secured on the cap on the opposite side of the head portion from the bellows, a second bellows mounted on the head portion to extend transversely to the movement of the first-mentioned bellows aNd actuating means engageable with the closed end and the second bellows for transmitting preselected movement of the closed end through the second bellows to the electrical translating means by radial distortion of the second bellows to thereby effect operation of the electrical translating means, in which the cap is secured to the body by a releasable connecting means, in which the connecting means includes means for relatively moving the cap with respect to the closed end of the bellows along the line of movement of the closed end to thereby enable adjustment of the position of the closed end of the bellows that operates the electrical translating means and in which the releasable connection includes a nut, cooperating threaded connectors on said nut and body and a flange formed on the cap and engageable by the nut.
 2. A differential pressure switch comprising a hollow body having an open end, a tubular bellows having a closed end and an open end, means securing the open end of the bellows to the interior of the body with the closed end being directed towards the open end of the body, means in said body for directing a first fluid to the interior of the bellows and a second fluid to the exterior thereof to have the differential pressure therebetween move the closed end of the bellows toward and away from the open end of the body, a cap secured to the body to close the open end thereof and having a head portion positioned within the body, electrical translating means secured on the cap on the opposite side of the head portion from the bellows, a second bellows mounted on the head portion to extend transversely to the movement of the first-mentioned bellows and actuating means engageable with the closed end and the second bellows for transmitting preselected movement of the closed end through the second bellows to the electrical translating means by radial distortion of the second bellows to thereby effect operation of the electrical translating means, in which the cap is secured to the body by a releasable connecting means, in which the connecting means includes means for relatively moving the cap with respect to the closed end of the bellows along the line of movement of the closed end to thereby enable adjustment of the position of the closed end of the bellows that operates the electrical translating means, in which there is compressible sealing means between the cap and the body and in which the releasable connection causes compression to be exerted on the sealing means to effect a seal.
 3. A differential pressure switch comprising a hollow body having an open end, a tubular bellows having a closed end and an open end, means securing the open end of the bellows to the interior of the body with the closed end being directed towards the open end of the body, means in said body for directing a first fluid to the interior of the bellows and a second fluid to the exterior thereof to have the differential pressure therebetween move the closed end of the bellows toward and away from the open end of the body, a cap secured to the body to close the open end thereof and having a head portion positioned within the body, electrical translating means secured on the cap on the opposite side of the head portion from the bellows, a second bellows mounted on the head portion to extend transversely to the movement of the first-mentioned bellows and activating means engageable with the closed end and the second bellows for transmitting preselected movement of the closed end through the second bellows to the electrical translating means by radial distortion of the second bellows to thereby effect operation of the electrical translating means, in which the cap is secured to the body by a releasable connecting means, in which the connecting means includes means for relatively moving the cap with respect to the closed end of the bellows along the line of movement of the closed end to thereby enable adjustment of the position of the closed end of the bellows that operates the electrical translAting means, in which the head portion includes stop means positioned to be engaged by the closed end to limit movement thereof after the translating means operating position and in which the stop means is positioned to limit the movement of the actuating means by the closed end after operation by the closed end.
 4. The invention as defined in claim 3 in which there is a second cap secured to close the other end of the body and having a head portion, second electrical translating means secured on the second cap on the opposite side of the second head portion from the bellows, a third bellows mounted on the second head portion to extend transversely to the movement of the first-mentioned bellows and second actuating means engageable with the closed end and the third bellows for translating preselected movement of the closed end through the third bellows to the second electrical translating means by radial distortion of the third bellows to thereby effect operation of the second electrical translating means and in which the head portion of the second cap carries stop means for limiting movement of the closed end and actuating means after operation of the second electrical translating means.
 5. The invention as defined in claim 4 in which the second cap is secured to the body by independently operable releasable connecting means. 